Hi, I've been having some problems with my high notes for the past three days or so. Usually, I am capable of a g (above the staff) to a b (one ledger line). A few weeks ago, my teacher had suggested I switch from a 7c to a 5c, and I did. I did not have any problems until now, which leads me to believe it is not the mouthpiece. Currently, I am getting a buzzing sound when I try to hit note between C (third space) and e (fourth space), I can't even produce anything above f. My trumpet teacher is away, so I will not have a lesson until two weeks later. Also, I find it difficult to produce the "buzz" on the mouthpiece alone. Any thoughts, advice, or help? I have an audition next Saturday!!